I thought of something. A narrow strip of sole leather, like about 1/4 to 3/8" wide, around the perimeter of the underside of the topsole, glued to it, then a layer of foam for the cushion, that fits between inside the leather perimeter. Then the midsole that will have channels for the adjustable straps to slide through for adjustments. I can find a suitable foam that will give enough for the topsole to conform to the shape of the foot. woohoo. That was easy. I'll use 6-7 ounce leather for all the layers: top sole, perimeter for the foam layer, mid sole for the straps to pass to the other side of the sandal, and the bottom sole. Then rubber sole. 5 layers. Every strap will be easily adjustable by the sandal owner. 100% adjustable. Actually all the straps will be made of one long piece of leather, not cut, but a continuous piece. When I had my shop 1970-1974, I made hundreds of pairs, and all of them had one continuous piece of strap leather, with channels, for the straps. The ankle posts, of course, were separate pieces.